Immutable Dictionary in C#

This post will discuss how to create an immutable dictionary in C#.

The ImmutableDictionary<TKey,TValue> class represents an immutable, unordered collection of keys and values in C#. However, you can’t create an immutable dictionary with the standard initializer syntax, since the compiler internally translates each key/value pair into chains of the Add() method.

1. Using `ToImmutableDictionary()` Method

We can use ToImmutableDictionary() method to construct an immutable dictionary from a sequence of key/value pairs. The following method demonstrates how to use the ToImmutableDictionary method for converting an existing mutable Dictionary<TKey,TValue> to ImmutableDictionary<TKey,TValue>.

using System;

using System.Collections.Generic;

using System.Collections.Immutable;

public class Example

{

public static void Main()

{

Dictionary<string, int> dict = new Dictionary<string, int>() {

{ "A", 1 }, { "B", 2 }, { "C", 3 }

};

ImmutableDictionary<string, int> immutableDict = dict.ToImmutableDictionary();

Console.WriteLine(String.Join(", ", immutableDict)); // [A, 1], [B, 2], [C, 3]

}

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2. Using `ImmutableDictionary<TKey,TValue>.Builder`

Another option is to create a new immutable dictionary builder ImmutableDictionary<TKey,TValue>.Builder and use the ToImmutable() method to construct an immutable dictionary based on the contents of the builder instance. For example,

using System;

using System.Collections.Immutable;

public class Example

{

public static void Main()

{

var builder = ImmutableDictionary.CreateBuilder<string, int>();

builder.Add("A", 1);

builder.Add("B", 2);

builder.Add("C", 3);

ImmutableDictionary<string, int> immutableDict = builder.ToImmutable();

Console.WriteLine(String.Join(", ", immutableDict)); // [A, 1], [B, 2], [C, 3]

}

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3. Using `ImmutableDictionary<TKey,TValue>.Add()` Method

Finally, you have the Add() method that adds the specified key/value pair to the immutable dictionary. Since it returns a new immutable dictionary that contains the additional key/value pair, we can chain multiple calls together. However, this approach is not preferable since it ends up creating a new immutable dictionary instance every time the Add() method is invoked.

using System;

using System.Collections.Immutable;

public class Example

{

public static void Main()

{

ImmutableDictionary<string, int> immutableDict = ImmutableDictionary<string, int>.Empty

.Add("A", 1)

.Add("B", 2)

.Add("C", 3);

Console.WriteLine(String.Join(", ", immutableDict)); // [B, 2], [C, 3], [A, 1]

}

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That’s all about immutable dictionary in C#.

Immutable Dictionary in C#

1. Using ToImmutableDictionary() Method

2. Using ImmutableDictionary<TKey,TValue>.Builder

3. Using ImmutableDictionary<TKey,TValue>.Add() Method

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1. Using `ToImmutableDictionary()` Method

2. Using `ImmutableDictionary<TKey,TValue>.Builder`

3. Using `ImmutableDictionary<TKey,TValue>.Add()` Method